Immobilised - help! Now solved

Looks like I/ve triggered the immobiliser somehow. My car is a 1992 XJ40 3.2 bought in 2008. Got it cheap with just one key fob and I also spotted that the previous owner had the security system switched off - the switch inside the glovebox. So I have just used the key operated central locking.

This morning for the very first time I had to get at the radio connections to see why the automatic antenna feed in the boot was dead. So I remove the ski slope, removed the six securing screws on the radio/climate control unit. But I could not get it out so gave up - very tight clearance with the shifter. Then (gulp!) I noticed that the radio display was dead. So I next tried the ignition and again no lights on the instrument panel and no starter! Checking other systems, lights, central locking, window lifts all still working fine.

It looks as if I have accidentally triggered the ignition immobiliser. A buddy who runs a local body shop (and who owns an XJ40 4.0 litre manual ) did manage to get the radio unit out. He carefully checked the connections - just one big multiplug and the antenna lead, nothing loose or damaged.

I dug out the old radio key fob, put a fresh battery in it and checked it was transmitting using a frequency meter and it was. This worked on the central locking (making “chirping” noises that I had never heard before) but failed to disarm the immobiliser.

We also checked some fuses - the instrument pack for example but nothing blown. There is a red led security light on the radio panel so are some of the alarm electronics inside it?

Anyone had something similar? It was a public holiday here in UK today but tomorrow I will need to move the car (in a public car park) so last chance to fix.

Can you help?

Many thanks,


Fuse A5 " Lighting Logic & Memories".
I must have grounded a wire in the boot messing with the electric antenna connections.
Replacing the fuse brought the radio display to life once more and she started on the button. But I still checked every one of the three banks of fuses to leave no doubt as to the cause.


Well done, I took the liberty of amending your header.